The Doctor and Amy encounter the Starship UK, a colony ship from an Earth that evacuated following devastating solar flares, containing all of the United Kingdom except Scotland, who wanted their own ship. On board, the Doctor attempts to comfort 12-year-old Mandy, whose silent tears are unacknowledged by the other passengers because, as the Doctor surmises, they already know what is wrong.
Amy follows Mandy and encounters a "hole" guarded by a keep out sign. Entering, she finds a tentacle-like creature and retreats to be confronted by four hooded figures, another of whom had previously reported the Doctor's presence to a masked woman. As the Doctor explores the engine room, the same masked woman appears to him. Introducing herself as Liz 10, she confirms his suspicion that the ship is flying without engines.
Amy regains consciousness in a voting booth. Here, as all adult travellers on the ship experience every five years, she is shown the truth behind Starship UK and then has to choose whether to "protest" or "forget" what she has seen. Amy chooses to forget, but not before recording a message to herself to get the Doctor back to the TARDIS and away from the ship. Amy does not inform the Doctor of this, and as he is unable to view the message due to not being human, he simply presses the "protest" button. This causes himself and Amy to be sent down a chute to the lower regions of the ship.
The Doctor and Amy land in the mouth of a large beast, which the Doctor causes to vomit and expel them to an overflow chute. Refusing to press a "forget" button and open the door to the main ship, they are attacked by two Smilers, the robotic creatures who keep watch over the ship. They are rescued by Liz 10, who reveals herself to be Queen Elizabeth the Tenth. She explains that she has been investigating the creature's infestation of the ship for her entire reign, working undercover against her own government.
The Doctor, Amy, Liz 10 and Mandy are then taken to the Tower of London, which is situated in the bowels of the ship, for investigating the beast. There it is revealed that the ship is powered by the last Star Whale, goaded by a ray penetrating its brain. The Doctor and Liz 10 are outraged at the cruelty being unleashed on the Star Whale, the latter demanding it be set free. Hawthorne, who had been guarding the creature in the Tower, reveals that Liz 10 ordered the situation in the first place.
In a video message, Liz 10 explains how the British people faced destruction when Earth was devastated by solar flares. The Star Whale appeared as a "miracle", and they captured it and used it to power their space ship. Liz 10 has to decide whether to forget, as she has unknowingly done every ten years for centuries, or abdicate, freeing the Star Whale and destroying the ship.
The Doctor realises that Amy chose to forget about the Star Whale so he would not face the choice between humanity and the alien. He then decides to render the Star Whale brain-dead, ending its suffering but still saving the humans on-board. Amy, however, sees the Star Whale's fondness for children and realises that its torture was unnecessary; it appeared to the UK's citizens in order to help them. She forces Liz 10 to press her "abdicate" button, and after a brief period of turbulence the Star Whale continues to transport the ship.
Amy explains to the Doctor that she recognised the Star Whale's kindness as the last of its race as comparable to his own as the last Time Lord. About to tell the Doctor of her impending wedding, she is interrupted by a call to the TARDIS from Winston Churchill, who is face-to-face with a Dalek.
* Matt Smith (Eleventh Doctor)
* Karen Gillan (Amy Pond)
* Sophie Okonedo – Liz 10
* Terrence Hardiman – Hawthorne
* Hannah Sharp – Mandy
* Alfie Field – Timmy
* Christopher Good – Morgan
* David Ajala – Peter
* Catrin Richards – Poem Girl
* Jonathan Battersby – Winder
* Chris Porter – Voice of Smilers / Winder
* Ian McNeice – Churchill
Writer Steven Moffat
Director Andrew Gunn
Script editor Brian Minchin
Producer Peter Bennett
Executive producer(s) Steven Moffat
Production code 1.2
Series 2010 series
Length 45 minutes
Originally broadcast 10 April 2010